Windows/DOS executable file (.sys)
.sys file signature | application/octet-stream
Windows/DOS executable file(SeeThe MZ EXE File Formatpage for the structure of an EXE file,with coverage of NE, TLINK, PE, self-extracting archives, and more.)Note:MZ are the initals of Mark Zbikowski, designer of the DOS executable file format.
High Risk Format
This file type can contain executable code. Always validate the source and scan with antivirus before opening.
Magic Bytes
Offset 0
4D 5A
Sources: Wikipedia, Gary Kessler
All Known Signatures
5 signature variants are documented for .sys files across multiple sources.
| Hex Signature | Offset | Sources |
|---|---|---|
| 4D 5A | 0 | Wikipedia, Gary Kessler |
| AA AA AA AA | 0 | Wikipedia |
| FE FF | 0 | Gary Kessler |
| FF 4B 45 59 42 20 20 20 | 0 | Gary Kessler |
| FF FF FF FF | 0 | Gary Kessler |
Extension
.sys
MIME Type
application/octet-stream
Byte Offset
0
Risk Level
High
Validation Code
How to validate .sys files in Python
def is_sys(file_path: str) -> bool:
"""Check if file is a valid SYS by magic bytes."""
signature = bytes([0x4D, 0x5A])
with open(file_path, "rb") as f:
return f.read(2) == signatureHow to validate .sys files in Node.js
function isSYS(buffer: Buffer): boolean {
const signature = Buffer.from([0x4D, 0x5A]);
return buffer.subarray(0, 2).equals(signature);
}How to validate .sys files in Go
func IsSYS(data []byte) bool {
signature := []byte{0x4D, 0x5A}
if len(data) < 2 {
return false
}
return bytes.Equal(data[:2], signature)
}API Endpoint
/api/v1/sys
curl https://filesignature.org/api/v1/sys
See the full API documentation for all endpoints and parameters.
Frequently Asked Questions
What is a .sys file?
A .sys file is a Windows/DOS executable file file. Windows/DOS executable file(SeeThe MZ EXE File Formatpage for the structure of an EXE file,with coverage of NE, TLINK, PE, self-extracting archives, and more.)Note:MZ are the initals of Mark Zbikowski, designer of the DOS executable file format.
What are the magic bytes for .sys files?
The magic bytes for Windows/DOS executable file files are 4D 5A at byte offset 0. These bytes uniquely identify the file format regardless of the file extension.
How do I validate a .sys file?
To validate a .sys file, read the first bytes of the file and compare them against the known magic bytes (4D 5A) at offset 0. This is more reliable than checking the file extension alone, as extensions can be renamed.
What is the MIME type for .sys files?
There is no officially registered MIME type for .sys files. Systems typically use application/octet-stream as a generic fallback when handling this format.
Is it safe to open .sys files?
Windows/DOS executable file (.sys) files are high risk because they can contain executable code. Never open .sys files from untrusted sources. Always scan with antivirus software, verify the source, and consider running in a sandboxed environment.